低维材料量子霍尔边缘态中畴界和马约拉纳零能态的探索和研究

Majorana Fermion, a peculiar type of Fermion, is its own anti-particle. Quasi-particles may exist in a number of solid state electronic systems that have properties of the Majorana Fermions, which are called Majoranan Zero Mode (MZM), Because of its non-Abelian statistics, MZM could be used in topological quantum computation. Based on previous experiments, the applicant plan to study the broken symmetry half-integer quantum Hall states (BSQHS) of ultra-high mobility graphene, with the support of this grant. The main focus will be to study the dynamics of different BSQHS, to look into the formation of zero-dimensional grain boundaries between BSQHS with Fermi parity and Bose parity, and to examine the MZM properties of such grain boundaries. The progress in this project would greatly deepen our understanding of BSQHS, benefit the search for the preparation and manipulation of MZM in quantum Hall systems, and have important academic and application values for the development of fault-tolerant topological quantum computation technology. The novelty of this project is that it uses Abelian half-integer quantum Hall states to create non-Abelian MZM, without the need to prepare the difficult-to-make 5/2 fractional quantum Hall states, nor does it require ultra-high quality superconductor/semiconductor and superconductor/topological insulator interfaces. The potential difficulties of realizing MZM is greatly reduced.

马约拉纳费米子作为一种奇异费米子，其反粒子就是本身。一些固体电子体系里可能存在符合马约拉纳费米子性质的准粒子，被称为马约拉纳零能态(MZM)。由于其符合非阿贝尔统计，MZM是一种可能用于拓扑量子计算的量子态。在申请人前期实验的基础上，拟研究超高迁移率石墨烯里面的完全对称性破缺的半整数量子霍尔态，并考察不同对称性破缺态演化的内在动力学过程，考察其中具有费米宇称和玻色宇称的边缘态之间零维畴界的形成规律，探索这类畴界的MZM特性。该项目的顺利推进将大大加深人们对特殊量子霍尔边缘态的理解，有益于探索在量子霍尔体系中制备和操控MZM的技术，对于容错的拓扑量子计算的发展具有重要的学术与应用价值。该项目的新颖之处在于其利用符合阿贝尔统计的半整数量子霍尔态的畴界制备非阿贝尔的MZM，不需要实现制备难度相当大的5/2分数量子态，或超高质量的超导体/半导体、超导体/拓扑绝缘体界面，项目实现难度相对较小。

通过该项目的资助，项目组成功实现了超高质量石墨烯/氮化硼异质结的制备以及对称性破缺量子霍尔绝缘态的可控制备，在前期研究的基础上（600mK样品温度，9T磁场下获得对称性破缺v=8态），成功实现了2K较高温度下，1T超低磁场下观测到v=8对称性破缺态。较高温度和超低磁场下观测到对称性破缺态对该量子态以后可能的应用非常重要，而该量子态的成功测量还依赖于项目组研发的精密电容测量系统，可以在低频（100KHz或以下）和高频（10MHz-100MHz）两个频段进行量子电容的低温强磁场精密测量。项目组进一步通过系统研究，发现偏置电流、垂直电位移场和外加磁场均对对称性破缺量子霍尔态有明显的调控作用，其中垂直电位移场的加大会破坏对称性破缺态，而对称性保持态有所增强。该项目的顺利推进拓展了人们对石墨烯对称性破缺态的制备能力、操控能力和理解，对探索其中特殊的对称性破缺态可能制备MZM具有支持作用。